This invention relates to a mobile station with transmission power control system.
In the field of cellular telecommunications, recent techniques have been directed to Code Division Multiple Access (CDMA) system, especially to Wideband CDMA (W-CDMA) system. In a CDMA system, a base station provides a cell-site (or a short cell-site) and communicates with multiple mobile stations of users existing on the cell-site. In the cell cite, each mobile station uses a channel identified by a uniquely assigned digital code. Therefore, communications between the base station and multiple mobile stations can be simultaneously carried out while sharing the same wideband frequency spectrum.
In a CDMA cellular system, transmission power levels of the mobile stations become important. A base station simultaneously receives the signals from many different mobile stations at the same frequency. The processes of CDMA demodulation taken into account, it is necessary that the signal received at the base station from each mobile station be as close as possible to single level. Otherwise, the signal from one mobile station overwhelms the signal from another mobile station. This problem is well known as near-far problem.
To resolve the near-far problem, a transmission power control of each mobile station is carried out in a CDMA cellular system so that the signal level received at the base station from each mobile station is as close as possible to a single predetermined level. Such transmission power controls are described in U.S. Pat. No. 5,056,109 and U.S. Pat. No. 5,940,743, the descriptions thereof incorporated by reference.
A transmitter including a transmission power control system comprises a plurality of parts such as amplifiers, filters, and a local oscillator. The characteristics of parts of a transmitter may be different from ones of parts belonging to another transmitter. That is, uneven quality may exist between transmitters. Additionally, the environment surrounding to a transmitter, especially temperature, has effects on the characteristics of parts of the transmitter. The uneven quality and the temperature effect cause a predefined power control system not to control the transmission power to be desired power. Therefore, it is necessary to compensate the uneven quality and the temperature effect.
In addition, the compensation must be designed not for instantaneous power of transmission but for average power of transmission at each slot. In a CDMA system, transmission signals are subjected not only to spectrum spreading but also conventional modulation for each slot. Therefore, demodulation requires no change of gain for each slot.
However, no transmission power control system can meet the foregoing requirements for compensation in the art.
It is therefore an object of the present invention to provide a mobile station having transmission power control system which can compensate the temperature effect and so on.
According to one aspect of the present invention, a mobile station has the following structure and transmits an output transmission signal for each of slots with power control. The mobile station comprises a transmission circuit, a signal extractor, a wave detector, a level data register, an error averager and a level corrector. The transmission circuit includes a variable gain amplifier, a signal processor, and a power amplifier. The variable gain amplifier is adapted to amplify a transmission signal with a gain controlled in accordance with a control signal to produce an amplified transmission signal, while the signal processor is adapted to process the amplified transmission signal into a radio frequency (RF) signal. The power amplifier is adapted to amplify transmission power of the RF signal to produce an amplified RE signal as the output transmission signal.
The signal extractor is arranged and is adapted to partially extract the output transmission signal to produce an extracted transmission signal over each slot. The wave detector is adapted to carry out a wave detection of the extracted transmission signal to produce a resultant signal of the wave detection. The level data register is adapted to output a level data signal indicative of a default controlled level of the output transmission signal. The an error averager is adapted to calculate for each slot an average error of the resultant signal of the level data signal to produce an average error signal. The level corrector is adapted to correct the level data signal with reference to the average error signal to produce a corrected level data signal corresponding to the control signal.
With the structure, the variable gain amplifier amplifies the transmission signal with a gain controlled in accordance with the corrected level data signal, to produce a gain controlled transmission signal which is transmitted as the output transmission signal through the signal processor and the power amplifier. Thus the mobile station can transmit the transmission signal with the power control of the transmission signal compensated for environment surrounding to the mobile station.